1. Field of the Invention
The present invention relates to osseodontic dental implant systems for tooth replacement in orthodontic patients.
2. Description of the Prior Art
In the field of orthodontics there are several techniques for tooth replacement. Crowns are widely employed for this purpose. However, dental crowns require a sturdy foundation. In the simplest, most desirable and least costly procedure the natural structure of the root of a tooth is utilized as the foundation to which the crown is anchored. However, in some instances, this is impractical since a tooth may be so badly damaged due to disease or injury that the entire tooth must be removed.
In such a situation one option is the use of an endosseous dental implant system. In such a system an implant member is inserted into the jaw of a patient. Very typically the implant member will be externally threaded with self-tapping screw threads that anchor the implant member into the bone of the jaw underlying the patient's gums. The implant member may be internally tapped to receive a fastening screw.
The implant member has opposing gingival and osseous ends. That is, the implant member is of a generally cylindrical, externally threaded configuration with an internally tapped blind bore therein. The open end of the bore is at the gingival end of the implant member which resides at the patient's gum when the implant member is installed. The opposite, osseous end penetrates into the bone structure of the patient's jaw.
A conventional osseous dental implant system also includes an abutment member. The abutment member also has opposing ends which may be referred to as the gingival and coping support ends. The gingival end of the abutment member faces and mates with the gingival end of the implant member. The abutment member includes an internal, longitudinal bore with openings at both of its ends and with a bearing ledge defined within its structure. A coping, which is an artificial tooth or crown, is ultimately permanently attached to the coping support end of the abutment. A screw is utilized to attach the abutment member to the implant member. The externally threaded shank of the screw extends through the longitudinal passageway defined through the structure of the abutment member and is threadably engaged with the internal threads of the blind, tapped bore in the implant member. The head of the screw rests upon the bearing ledge in the structure of the abutment member to firmly, and ultimately permanently, attach the abutment member to the implant member.
A conventional endosseous dental implant fastening screw is formed with a head having a cylindrical outer surface configuration and a shank of smaller diameter externally threaded with male, right-hand threads throughout its length. At the center of the top of the head a socket or cavity of noncircular cross section is formed to receive the distal end of a fastening tool. Very typically the socket has a hexagonal cross-sectional shape, as does the distal tip of the fastening tool. The slender shank of the fastening tool fits within the narrow passageway formed through the abutment and the hexagonal tip at the distal end of the fastening tool engages the walls of the socket in the screw head so as to allow the screw to be rotated by turning the grip of the fastening tool. The shank of the fasting tool is slender enough to fit into the narrow, open end of the passageway formed through the abutment.
With the distal tip of the fastening tool engaged in the socket of the screw, the screw is inserted into the abutment passageway and guided longitudinally along until the externally threaded shank of the dental implant fastening screw reaches an internally threaded, necked-down region of the abutment passageway. This necked-down region forms an outwardly facing, annular bearing ledge that forms a seat for the underside of the head of the dental implant fastening screw adjacent its shank.
By rotating the fastening tool in a clockwise direction, the right-hand, spiral threads of the fastening screw are advanced into engagement with the internal, female threads at the necked-down region of the abutment passageway. Advancement of the fastening screw is continued by rotating it in a clockwise direction until the distal extremity of the dental implant fastening screw reaches the internal threads of the dental implant member. Continued clockwise rotation of the fastening tool advances the threads on the shank of the dental implant fastening screw into engagement with the internal threads of the dental implant. Tightening is continued in this manner until the annular face of the head of the dental implant fastening screw adjacent the shank thereof arrives in abutting relationship against the annular screw seat defined within the abutment in the longitudinal passageway that extends through the entire length of the abutment. Because the distal tip of the fastener installation tool has a noncircular cross section that fits snugly into a socket in the screw head of a corresponding shape, continued rotation of the grip securely tightens the threads of the dental implant fastening screw into the mating, female threads of the dental implant. Once the fastening screw has been tightened, the tip of the fastener installation tool may be pulled longitudinally out of the hexagonal socket defined in the exposed end of the head of the dental implant fastening screw.
While a conventional dental implant screw fastener installation tool operates quite well to tighten dental implant fastening screws in position, it is sometime necessary to remove the dental implant fastening screw for various reasons. In conventional practice the same fastener installation tool is employed. That is, the distal, hexagonal tip of the fastener installation tool is inserted into the corresponding hexagonal-shaped socket formed in the head of the fastening screw and the grip of the fastener installation tool is counterrotated, in a counterclockwise direction. The shank of the dental implant fastening screw is thereupon threadably disengaged from the female threads of the dental implant member, and subsequently from the female threads of the abutment.
The progressive withdrawal of the fastening screw proceeds without difficulty as long as there is engagement between the threads of the fastener screw and those of either the implant or the abutment. However, at some point the threads on the shank of the fastening screw disengage completely from the internal threads in the necked-down region of the abutment. This disengagement typically occurs well before the head of the fastening screw is accessible from outside the passageway opening of the abutment.
Without thread engagement during counterclockwise rotation of the fastening screw relative to the abutment, there is no force urging the fastening screw out toward the open end of the abutment passageway, even if the rotation of the fastener installation tool in a counterclockwise direction is continued. To the contrary, while the fastening screw can be rotated, it rotates freely within the confines of the smooth-walled cylindrical portion of the passageway and cannot easily be withdrawn further. If one attempts to merely withdraw the shank of the fastening tool out of the open end of the passageway in the abutment, the hexagonal tip at the distal end of the fastening tool is merely pulled longitudinally out of the hexagonal socket, leaving the fastening screw within the confines of the longitudinal passageway through the abutment.
In a typical conventional practice, it is necessary to create some type of frictional engagement between the distal tip of the fastener installation tool and the socket in the head of the fastening screw in a longitudinal direction. This is sometimes achieved by inserting a toothpick longitudinally into the open end of the passageway alongside the shank of the fastening tool to attempt to grip some location on the peripheral end of the head of the fastening screw between the toothpick and the shank of the fastener installation tool. That is, the shank of the fastener installation tool and the toothpick are utilized somewhat in the manner of tongs to attempt to grip a peripheral location on the head of the fastening screw to allow complete withdrawal of the fastening screw from the abutment passageway. This procedure is somewhat awkward and requires considerable practice to master the technique.
Another approach that has been taken is to put a small amount of wax on the end of the distal tip of the fastener installation tool before the shank of the fastener installation tool is inserted into the socket formed in the dental implant fastening screw head. The wax acts as sort of a temporary adhesive between the distal tip of the fastening tool and the socket in the dental implant screw head. However, this technique also requires considerable patience, since the adhesive bond of the wax to the fastening tool and to the socket of the screw head is necessarily quite weak.